This invention pertains to a process for plating a metal such as copper or nickel on an article fabricated from a platable resin, which may be any of a variety of resins including polypropylene as well as acrylonitrile-butadiene-styrene copolymers, polyaryl ethers, polycarbonates, polyethylene, and other resins in common engineering use.
Conventionally, an article molded of a platable grade of acrylonitrile-butadiene-styrene copolymer (ABS) or other resin is plated by one of various processes requiring the article to be cleaned, etched in a strong acid, and sensitized in an acidic solution of tin salts, palladium salts, or other compounds, which act as catalysts for subsequent deposition of a metal in a bath by immersion or by reduction of the metal from a complex. Commonly, the strong acid is chromic acid, either with or without sulfuric acid. Typical steps of such processes are given by H. M. Goldman, "Electroplating," Modern Plastics Encyclopedia 1979-1980, Volume 56, Number 10A, McGraw-Hill, Inc., New York, October 1979, at pages 436-437.
Other references of pertinent interest include: D. W. Himler and J. A. Alzapiedi, "Preparing Plastics for Plating," SPE Journal, Vol. 29, June 1973, at pages 57-60; E. J. Stefanides, "Electroplated ABS Parts," Design News, March 3, 1965; "Electroplating `the unplatables,`" Modern Plastics, November 1967, at pages 98-101; C. E. MacNeill and G. T. Chiurazzi, "Plated Plastic Parts," Materials in Design Engineering, November 1962, at pages 122-125; H. L. Pinkerton, "Preparing Nonconductors for Electroplating," Chapter 28 in F. A. Lowenheim, Editor, Modern Electroplating, 2nd Edition, John Wiley & Sons, Inc., New York, copyright 1963, at pages 604-617; and E. B. Saubestre, "Plating on Nonconductors," Chapter 28 in F. A. Lowenheim, Editor, Modern Electroplating, 3rd Edition, John Wiley & Sons, Inc., New York, copyright 1974, at pages 636-655.
Various chemical and mechanical processes for metallizing of plastics are considered in H. Narcus, Metallizing of Plastics, Reinhold Publishing Corporation, New York, copyright 1960. As considered by H. Narcus, op. cit., at pages 148-159, such processes include spraying of heated metal particles in compressed air.
It is known that trichloroethylene softens (swells) many resins although not polypropylene, but use of trichloroethylene in plating on resins has been restricted. A process wherein an article is immersed successively in a solution containing trichloroethylene, ethanol, and phosphorous sesquisulfide, and in a solution of copper pyrophosphate so as to produce what is described as "a red conductive copper-phosphorus-sulfur coating", before the article is electroplated initially with nickel and subsequently with chrome, is disclosed in U.S. Pat. No. 3,650,708 to W. P. Gallagher. A process wherein an article is immersed in a bath containing trichloroethylene, white phosphorous, an anionic blend of alkaryl hydrotopes, and sodium dodecyl diphenyl ether disulfonate, is disclosed in U.S. Pat. No. 3,647,512 to J. J. Grunwald et al.
However, there remains a need, to which this invention is directed, for a process which is simple, fast, inexpensive, and effective for plating on a variety of plastics, which does not require chromic acid either with or without sulfuric acid, and which does not require initial deposition of a metal by catalytic reaction.